Monday, May 25, 2009

In our everyday myriad insignificant living day in and day out, maybe we have stopped asking some basic questions we use to intrigue ourselves regularly “when we were young”. It is often reflected when I go for my fortnightly visit to my barber – I ask him incessantly “am I going bald” – he normally reverts back asking “is your father bald” – my answer is a blank stare and rhetoric pause and the emphatic NO soon follows suit.

If I am so obsessed with asking if I were going bald, why not excite myself with the most common desert view I see regularly and try to pique myself to find out why it happens. My uncle use to give me money for buying books – the first instalment of money put together and I bought a series called “TELL ME WHY” – and later argue endlessly with my childhood and still friends Bedanta lovingly called “bedu” on various unnatural phenomenon and common unscientific Harry Houdini stuff.

It took Ani while swinging in the back seats of my frowning Mitshubishi Lancer to look out the window and ask all of us “What is that phenomenon called”, we instantly chorus voiced “it’s a MIRAGE”, on being prodded why – I simply answered back “it’s an optical illusion” and then came the million dollar question “WHY DOES IT HAPPEN”

I simply couldn’t reach out to my “TELL ME WHY” collection in the old dusted library lying near my low lying bed in my bedroom few oceans and mighty rivers away in India (Assam – Duliajan). They have been long forgotten and married to fine dust.

Shubha and her father too tried with similar results. So, here I am going back to finding out WHAT IS AN MIRAGE? And here’s what I found out – this time googling away to glory.

Wiki says: “A mirage is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky. In contrast to a hallucination, a mirage is a real optical phenomenon which can be captured on camera, since light rays actually are refracted to form the false image at the observer's location”

You see it not only in desert but also hot summer days in your lane as well, false impression of water reflecting from the surface – as scientist and ignorant observers say, it is also seen in Polar Regions albeit with different effect. We will come into that later, but first a little primer in physics you ignorant adult communion!!

“Mirage occurs due to total internal reflection of light. When the sun is high in the sky, the sand gets heated first and then the layers of air above it. The rays from the trees travel from an optically denser air layer to a rarer layer and hence bend away from the normal. This bending continues and a stage is reached where the angle of incidence becomes greater than the critical angle and total internal reflection takes place”

Need any illustrated diagrams we used to draw with a scale and pencil rubbing our running noses:

Wiki adds: “The model given above explains the cause of the inferior mirage, called "inferior" because the image seen is under the real object. The real object is the (blue) sky or any distant object in that direction, meaning we see a bright bluish patch on the ground in the distance. For exhausted travelers in the desert it appears as a lake of water. On tarmac roads it may seem that water or even oil has been spilled. This is called a "desert mirage" or "highway mirage".

Now since you know why it happens in desert and the whole funda about warm air and cold air – what really happens in roads while we drive something which Ani noticed!! How come water appears in the distant highway?

A highway mirage is an inferior mirage which can be seen very commonly on roadways by day or by night. The hot-road mirage is usually most noticeable on hot sunny days.

Warm air is less dense than cool air, and the variation between the hot air at the surface of the road and the denser cool air above it creates a gradient in the refractive index of the air. Light from the sky at a shallow angle to the road is refracted by the index gradient, making it appear as if the sky is reflected by the road's surface. The result looks to the human mind like a pool of water on the road, since water also reflects the sky

Now let’s talk about the other phenomenon – also called superior mirage often seen in polar “chill” regions.

Going back to wiki: “Superior mirages are most common in polar regions, especially over large sheets of ice with a uniform low temperature. They also occur at more moderate latitudes, however, although in that case they are weaker and not so smooth. For example a distant shoreline may be made towering, looking higher (and thus perhaps closer) than it is in reality, but because of the turbulences there seem to be dancing spikes, towers and so forth. This type of mirage is also called the Fata Morgana or, in Icelandic, halgerndingar.”

Now you know why MIRAGE happens – Ani this goes for you for bringing back the TELL ME WHY avatar in me long known to be dead!!

1 comments:

great! thanks for explaining it so well in simple terminology. i used to be a tell me why freak too reading stuff like "why does the moon follow you when you are in a moving car?" things we just notice and then let go.